Interpretive Summary: Stripe rust of wheat is most destructive in the United States and many other countries. Developing cultivars with non-race specific and durable resistance is essential for sustainable control of the disease. Spring wheat cultivar ‘Express’ has both race-specific all-stage (also called seedling and overall) resistance and high-temperature, adult-plant (HTAP) resistance to stripe rust, The HTAP resistance is non-race specific and durable. We have previously published genetics and molecular mapping of the race-specific all-stage resistance in Express. In this publication, we report quantitative trait loci (QTL), genes for quantitatively inherited traits, for HTAP resistance in the cultivar. Three QTL were identified with significant additive effects on HTAP resistance, explaining 49.5% to 69.6% of the phenotypic variation for disease severities. Two of the QTL explained 30.8% to 42.7% of the phenotypic variation for infection types. Significant effects between gene interactions were detected, which increased the total explained phenotypic variation by 1.7 to 3.6%. The three QTL were mapped to wheat chromosomes 6AS, 3BL, and 1BL. The QTL on 6AS and 3BL had higher effects than the QTL on 1BL and therefore, should be more useful. The markers for the QTL on 6AS and 3BL were highly polymorphic in 44 tested wheat genotypes, indicating that these markers should be useful in introgressing and pyramiding the HTAP resistance QTL into other wheat cultivars.

Technical Abstract:
Wheat cultivar Express has durable, high-temperature adult-plant (HTAP) resistance to stripe rust (Puccinia striiformis f. sp. tritici). To elucidate the genetic basis of the resistance, Express was crossed with ‘Avocet Susceptible’ (AVS). A mapping population of 146 F5 recombinant inbred lines (RILs) was developed using single-seed descent. The RILs were evaluated at two sites near Pullman in eastern Washington and one site near Mount Vernon in western Washington in 2005, and were evaluated near Pullman in 2006 under natural stripe rust infection. Infection type (IT) and disease severity (DS) were recorded three times for each line during each growing season. The DS data were used to calculate relative area under the disease progress curve (rAUDPC). Both IT and rAUDPC data showed continuous distributions, indicating the Express HTAP resistance was controlled by quantitative trait loci (QTL). Resistance gene analog polymorphism (RGAP) and simple sequence repeat (SSR) techniques were used to map the HTAP resistance QTL. Three QTL were detected with significant additive effects, explaining 49.5% to 69.6% of the phenotypic variation for rAUDPC. Two of the QTL explained 30.8% to 42.7% of the phenotypic variation for IT. The three QTL were mapped to wheat chromosomes 6AS, 3BL and 1BL, which were designate as QYrex.wgp-6AS, QYrex.wgp-3BL and QYrex.wgp-1BL, respectively. QYrex.wgp-6AS, and QYrex.wgp-3BL, which had higher effects than QYrex.wgp-1BL, were different from previously reported QTL/genes for adult-plant resistance. Markers Xgwm334 - Xwgp56 and Xgwm299 - Xwgp66 flanking the two major QTL were highly polymorphic in various wheat genotypes.